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An empirical subgrouping of finnish learning-disabled children Tapio T. Korhonen



Pediatric Clinic, University of Turku , Finland Published online: 04 Jan 2008.

To cite this article: Tapio T. Korhonen (1991) An empirical subgrouping of finnish learningdisabled children, Journal of Clinical and Experimental Neuropsychology, 13:2, 259-277, DOI: 10.1080/01688639108401042 To link to this article:

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Journal of Clinical and ExperimentalNeuropsychology 1991, Vol. 13, NO. 2, pp. 259-211

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An Empirical Subgrouping of Finnish Leaming-Disabled Children"

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Tapio T. Korhonen Pediatric Clinic, University of Turku, Finland

ABSTRACT The internal and external validity of a subgrouping of 82 Finnish children with relatively mild learning disabilities and 84 Controls was explored. The sample was selected from a total population of 1607 second grade pupils. Eight neuropsychological measures from four function areas were selected as classification criteria in cluster analysis. Six consistent and clinically meaningful subgroups were derived. These subgroups were designated as follows: (1) Normal, (2) General Language, (3) Visuo-Motor, (4) General Deficiency, (5) Naming, and (6) Mixed. Most of the LDs were clustered in subgroups (2) through (6); and most of the Controls, in subgroup (1). Several internal and external validation procedures indicated at least moderate validity in the subgroups, with the exception of the Mixed subgroup. The five valid subgroups encompassed 82 % of the LDs and 90 % of the Controls and, moreover, resembled subgroups which previously have been found among English-speaking children. This suggests that language differences exert no significant effect on the types of the emerging subgroups.

It is widely accepted that learning disability (LD) or reading disability in children constitutes a heterogeneous diagnostic entity (Hynd & Willis, 1988; Satz, Morris, & Fletcher, 1986; Rourke, 1983). Several researchers have attempted to develop typologies of LD children, either through clinical inspection of testresults (Boder, 1973; Mattis, Rapin, & French, 1975) or through application of multivariate strategies (Jhehring, Trites, Patel, & Fiederowicz, 1981; Lyon, Stewart &Freeman, 1982; Morris, Blashfield, & Satz, 1986; Peuauskas & Rourke, 1979; Satz & Morris, 1981; Spreen & Haaf, 1986; Watson & Goldar, 1988).

This paper is based on a Ph.D. dissertation completed at the University of Turku, Finland. Portions of this paper were presented at the meeting of International Neuropsychological Society in Copenhagen, 1985, and New Orleans, 1988. I gratefully acknowledge the helpful comments of Paul Satz and Robin Morris on earlier drafts of this paper, and George W. Hynd for reading and commenting on the manuscript for this paper. The study was partially supported by The Academy of Finland. Address for correspondence: Tapio T. Korhonen, Ph.D., Pediatric Clinic, University of Turku, SF-20520 Turku, Finland. Accepted for publication: June 16, 1990.

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The main findings of these studies are consistent with those theoretical neuropsychological models suggesting that higher level cognitive processes, such as reading and writing (spelling), take place through the interaction of several cortical and subcortical functions forming functional systems (Benson, 198 1; Hynd & Hynd, 1984; Luria, 1973). Any deficit or delay in the development of the brain regions involved in reading or writing may contribute to a breakdown of these functions (Luria, 1973). Theoretical models of reading and writing stress the role of the left hemisphere and linguistic processes, while also noting the active role of the right hemisphere. Studies to this point have usually identified at least one verbal subtype, one spatial subtype, and a mixed verbal-spatial subtype. However, no general consensus has emerged regarding the quantity or quality of the “real” subtypes to be used to define LD (Doehring, 1984). Hence, studies exploring the validity of LD subtypes in different populations are still needed. Except for the studies of Lundberg (1985) in Sweden, Van der Vlugt and Satz (1985) in Holland, and the preliminary report of Gjessing (1986) in Norway, statistical subtype studies published thus far have involved English-speaking children. The Finnish language differs from English in that Finnish graphemephoneme correspondence is nearly perfect. It could be hypothesized, on the one hand, that such a difference in the language could impact on the nature of the LD subgroups. On the other hand, the evidence from the clinical-inferential subtype studies of Gjessing (1986) and the statistical study of Van der Vlugt and Satz (1985) suggest that similar subgroups of LD children may also exist in nonEnglish language groups. Thus, there exists some cross-cultural evidence supporting the generality of LD subtypes. Particularly critical to subtype research is the question of whether LD subtypes differ neuropsychologically from age-matched children with no learning problems. Weener (1981) reported a noticeable overlap in test performances between LD subjects and normal learners. However, in the majority of studies, only LD subjects, o r , at most, only small groups of control subjects have been included in the subgrouping. The studies of Petrauskas and Rourke (1979), Decker and DeFries (1981), and Morris et al. (1986), each of which included control subjects in the subgrouping procedure, suggest that there are both quantitative and qualitative differences between LD subgroups and control subgroups. Further, most of the studies have been undertaken with clinically referred or otherwise highly selected samples of LD children ( Doehring et al., 1981; Lyon, Stewart, & Freeman, 1982; Petrauskas & Rourke, 1979; Satz & Morris, 1981). It may well be that these subjects have rather severe learning disabilities. No studies have so far been undertaken to characterize the LD subtypes of children with mild LD as compared to the subtypes found in clinical samples of LD chiidren. The importance of the external validation of the empirically derived subgroups, in addition to their internal validation, has been stressed (Fletcher, 1985; Skinner, 1981). With the exception of the Satz and Morris (1981) investigation, external validity studies of neuropsychological subgroups of LD children using

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behavioral variables are still lacking. In their study, Satz and Moms (1981) analyzed the subgroups using the Children’s Personality Questionnaire (Porter & Cattell, 1972), but the results failed to separate the subgroups. The results of some earlier subtype studies (Rutter & Yule, 1975; Satz & Morris, 1981) have suggested that the following are overrepresented in subgroups with general neuropsychological disorders: families with low occupational status, girls, the youngest subjects, and subjects with neurological soft signs as compared to subgroups with more specific disorders. These findings enable some speculations concerning possible explanations of the results. Witelson (1977) has proposed that the brain of the young female is more diffusely organized than is that of the young male and, therefore, less prone to the possible adverse effects of cerebral dysfunction. It also might well be that the effects in girls are more generalized than are those in males. Further, general neuropsychological disorders very probably diminish the IQ. On the other hand, neurological symptoms are often accompanied by low IQ (Rutter & Yule, 1975). Thus, there may be a relationship between general neuropsychological disorders, low IQ, and neurological symptoms. It would also be expected that the relationship generally found between low social class and relatively low IQ would reflect a generally slower development rather than more specific disorders. Again, if some of the LD children could best be described as suffering from a general developmental lag, from which they possibly would “catch up” during development (Satz, Fletcher, Clark, & Morris, 198l), then there should be more such children among the youngest subjects compared to the older subjects. The aim of the present study was to determine whether it is possible to divide a group of Finnish-speaking children with mild LD and a matched control group into reliable and valid subtypes, using a multivariate classification method applied to neuropsychological test results. A further aim was to determine whether the subgroups resemble those found in earlier studies using English-speaking children. Based on the previous discussion, the following hypotheses were formulated: (1) It is possible to identify at least one verbal subtype, one spatial subtype, and one mixed verbal-spatial subtype in the LD sample. (2) These subtypes differ neuropsychologically from subtypes of age-matched children with no LD. ( 3 )Girls, subjects with neurological soft signs, the youngest subjects, and subjects from families with low occupational status, as compared to subtypes with more specific disorders, would be overrepresented in subtypes with rather general neuropsychological disorders.

METHOD Subjects The primary sample was drawn from a population of 1607 children (799 boys, 808 girls) born within one calendar year. At the beginning of the study, all subjects were in a regular second grade classroom or in a small, special second grade class for children with perceptual disorders. The schools were located in Turku, Finland, a city with approximately 160,000 inhabitants.

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The present study applied the definition of LD as defined by the Joint Committee on Learning Disability (Hammill, Leigh, McNutt. & Larsen. 1981). In this study, Learning Disability was operationally defined as a condition in which a child demonstrated difficulties with reading, writing (spelling), or mathematics to such an extent that the classroom teacher. in cooperation with a special teacher for reading and writing, agreed that remedial teaching, in addition to regular class instruction, was warranted. Moreover, a third teacher must have concurred with this designation about 8 months later, during the third school year. Unfortunately, there are no standardized achievement tests available in the Finnish language. This is a limitation precluding exact comparison with other studies. This limitation, however, was not judged to invalidate the results of the present study. The Finnish school system is very homogeneous, implying that not only the instructions which the children receive but also the rating principles are highly uniform in quality, even from school to school. In most cases, the classroom teachers had taught the same children for nearly two years and were, therefore, thoroughly familiar with the skills of their pupils. Thus, it is reasonable to believe that the teacher ratings were fairly reliable. The teacher ratings of the severity of the difficulties in reading. writing, and mathematics in the final LD group are given in Table 1. To avoid possible extreme cases, children with a Full Scale IQ (WISC-R)less than 80, children with clear neurological diseases, and children coming from very extreme family situations (e.g.. asocial families) were excluded. The selection of the learning disabled subjects (LD) and the controls (C) occurred in three phases.

Phase I . In the spring of the second school year, a request was sent to all the teachers to designate the children with LD. Fifty-six of the 65 teachers from 27 of the 36 schools reported 173 children (62 % boys) with learning problem. Phose 2. About one month later, the special teachers for reading and writing disabilities were requested to rate, in cooperation with the regular classroom teachers, the seventy of the difficulties of the 173 pupils in reading, writing, and mathematics. Utilizing the information received during these first two phases, 36 of the 173 children were excluded from the LD group based on the adopted definition of LD. The remaining 137 children (8.5 5% of the primary population) were asked to participate in individual examinations. Parents of 41 subjects refused to cooperate for various reasons. This group of children ( n = 41) did not differ significantly in x*-analysis from those who accepted the proposal ( n = 96) in regard to sex, father’s occupational class, or the teacher ratings of the severity of the disability in reading and writing (spelling).

Phase 3 During the middle of the third grade year, new class teachers were requested to rate the LD of the 96 children using a 4-point scale (1 = no difficulty, 2 = slight difficulty, 3 = great difficulty, 4 = very great difficulty). The criterion for inclusion in the final LD group was the teacher rating of at least 3 in either reading or writing or alternatively a rating of 2 in both areas. In this phase, 14 subjects were excluded.The final number of subjects in the LD group was 82. The general characteristics of the children with LD are given in Table 1. Selection of the control subjects: In the first phase of the subject selection procedure, each teacher named 2 control children for each of the 173 LD subjects, by selecting from the same school classes the two pupils in the next alphabetic order with the same sex and with no learning disorders. In Phase 2, ninety-six Cs were matched with the LD group according to sex and the fathers’s occupational status. Of this group, 4 subjects refused to cooperate. In the third phase, 8 additional subjects were excluded. Six had slight problems with learning in the third grade, according to the teacher ratings. One had a Full Scale WISC-R IQ of less than 80, and 1 was severely emotionally disturbed. The final C group consisted of 84 children ( see Table 1).



Table 1. Characteristics of LD and Control Group Control Group (n = 84)

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LD Group (n = 82) Boys Girls Age in months (mean) Father’s occupational status class 1 class 2 class 3 WISC-R Full Scale IQ WISC-R Verbal Scale IQ WISC-R Performance Scale IQ Reading-Error score Writing-Error score Absences from school ( hoursflast term) Teacher ratings of the LD groupd Severe difficulties Mild difficulties No difficulties


50 32 113.7 (4.9) a

34 116.2 (3.8)***

7 60 15 97.7 ( 9.6) 92.9 (10.4) 103.8 (1 1.6) 18.7 (13.6) 19.4 (13.7) 10.8 (10.9)

3 62 9 110.2 (12.5)”’ 106.8 (11.1)*** 112.2 (14.1)*** 4.1 ( 4.4)*** 5.1 (4.8) 13.6 (18.9)

reading 73 % 24 % 3%

writing 82 % 18 %


mathematics 51 % 28 % 21 %

Notes: ‘Standard deviation bRauhala (1966) cRuoppila et al. (1968, 1969) dTeachersused a 1-4 scale (l=no problems, 2=some problems, 3=severe problems, 4=very severe problems). A rating of 1 was here labeled as “no difficulties”, a rating of 2 as “mild difficulties”, and a rating of 3 or 4 as “severe difficulties”. *** LD group/Control group difference is significant at the level p.Although the Normal subgroup had the lowest error score, the Tukey comparison showed that the difference between the Normal and General Language subgroups was not significant. The differences


27 1

between the Normal subgroup and all other subgroups were significant. The differences among the Visuo-Motor, General Deficiency, and Naming subgroups were not statistically significant.

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( 5 ) Neurological soft signs: Using the criterion of two or more indisputable neurological soft signs, the four LD subgroups had, in general, more children meeting the criterion than did the Normal subgroup (Table 3). All subgroups, except the General Language subgroup, differed significantly from the Normal subgroup (the Fischer-test: Visuo-Motor vs. Normal pe.05; General Deficiency vs. Normal p

An empirical subgrouping of Finnish learning-disabled children.

The internal and external validity of a subgrouping of 82 Finnish children with relatively mild learning disabilities and 84 Controls was explored. Th...
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